This looks like ell grass that I just spotted in my pond this morning. I planted Corkscrew Ell Grass 8 feet apart around the pond about three weeks ago but only single plants. My planted ell grass looks and lays bent on top of the water just like the ones in the picture. So I was wondering how this got here. Ducks set on the log so maybe their poo had seeds in it. At any rate I'm glad to have the extra ell grass if that is what it is.